MArray Constructor should make copy

[garrison]

As discussed on discourse (and following the conclusion in JuliaLang/julia#23107), the MArray constructor should return a copy if an MArray is passed to it, but it does not in StaticArrays v0.6.4:

julia> a = @MVector [1,2,3]
3-element MVector{3,Int64}:
 1
 2
 3

julia> MVector(a) === a
true

[c42f]

Thanks for the bug report. This should be fixed now in master.

[garrison]

Thank you!